1. Field of the Invention
This invention relates to an aircraft position light. Specifically, the invention is directed to a position light that uses light sources and a prismatic optic array.
2. Description of the Related Art
Aircraft operating at night utilize a variety of lights to attract the attention of other aircraft operating in the same airspace, in order to prevent collisions between aircraft. One such lighting system is the position lighting system.
A position lighting system comprises a red light installed on the port wing, a green light installed on the starboard wing, and one or more white lights installed at a rearward-facing position on the aircraft. Other aircraft operating in the vicinity of the lighted aircraft can discern the relative position of the lighted aircraft and its direction of travel by the color of the observed position lights and their movement, allowing the other aircraft to take evasive action as needed to avoid a collision.
Position lights have previously been installed on aircraft for this purpose, but they suffer from several disadvantages. Prior position lights use incandescent lamps, which have a limited life. This limited life is further reduced by the harsh aircraft operating environment. Because aviation safety regulations require functioning position lights when operating at night, failure of the position lights can result in delayed flight departures in addition to the high maintenance costs associated with frequent lamp replacement. Some improvements in aircraft lamp life have been made by the use of at least one light emitting diode (LED), such as the aeroplane cabin lighting arrangement described in Fleischmann U.S. Pat. No. 6,203,180. However, position lights require additional considerations, as will be discussed below.
Another disadvantage with the use of incandescent lamps in the design of position lights is the difficulty encountered in designing small and efficient optical systems that provide sufficient illumination in both the horizontal and vertical planes relative to the position light, while properly limiting light distribution. Such light limiting, known as “angular cutoff,” is necessary to prevent excess overlap between the position lights on the aircraft so that other aircraft operating in the same airspace can accurately discern the lighted aircraft's individual position lights, assisting in determination of its relative position.
It is known that prisms may be used to direct and diffuse light. For example, in Hutchisson U.S. Pat. No. 5,325,271, a marker lamp having LEDs and a prismatic diffuser is disclosed. However, this system utilizes openings in the input facets of the prism to mount the LEDs into the prism. This configuration does not permit the arrangement of LEDs into a single plane, which would reduce complexity and cost. Further, this system is concerned with the diffusion of light and does not teach how to produce an asymmetric lighting pattern having a sharp cutoff, as is needed for aircraft position lights. In Maurer U.S. Pat. No. 4,161,770, a prism is disclosed for a guide signal device. Light emitted from the source undergoes total internal reflection before emerging at one of the surfaces of the prism. The prism thus permits the guide light to be of low-profile construction, yet visible at a distance. However, the system disclosed by Maurer does not teach how to utilize both direct light emission and total internal reflection to produce the necessary sharp angular cutoff and the asymmetric lighting pattern needed for aircraft position lights.
To compensate for their drawbacks, prior position lights utilize multiple incandescent lamps to offset the short lamp life, and complex reflector arrangements to achieve the required light distribution. There is a need for a position light which provides the necessary light distribution and long operating life in the harsh aircraft environment.